[InstCombine] Remove unused llvm.experimental.noalias.scope.decl

A @llvm.experimental.noalias.scope.decl is only useful if there is !alias.scope and !noalias metadata that uses the declared scope.
When that is not the case for at least one of the two, the intrinsic call can as well be removed.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D95141